Add lower-constraints job to current development branch

The lower-constraints test was removed because of an issue where pip
could not correctly determine the required packages versions to install,
ending in an almost infinite loop that would end up in timeout, failure,
and general mayhem.
Recently the issue has been fixed and, if properly configured, the
lower-constraints test can provide good indication of which minimum
versions are required to support the current code.
This patch adds the test back to the current development branch, and it
runs only on master.
The lower-constraints file will stay in the future stable branches.

Change-Id: Ic9cef3e56266c6e9de0936b5f113e8b38d705a9b

lower-constraints.txt

@@ -0,0 +1,26 @@
+Pint==0.5
+Werkzeug==1.0.1
+bandit==1.1.0
+coverage==4.0
+cryptography==2.3
+dogpile.cache==0.9.2
+eventlet==0.18.2
+importlib_metadata==1.7.0;python_version<'3.8'
+ironic-lib==4.7.1
+netifaces==0.10.4
+openstacksdk==0.49.0
+oslo.concurrency==3.26.0
+oslo.config==5.2.0
+oslo.log==3.36.0
+oslo.serialization==2.18.0
+oslo.service==1.24.0
+oslo.utils==3.33.0
+oslotest==3.2.0
+pbr==2.0.0
+psutil==3.2.2
+pyudev==0.18
+requests==2.14.2
+stestr==1.0.0
+stevedore==1.20.0
+tenacity==6.2.0
+testtools==2.2.0

tox.ini

@@ -137,3 +137,9 @@ commands =
   pip install -e {toxinidir}/examples/business-logic
   pip install -e {toxinidir}/examples/vendor-device
   python -c 'import example_business_logic; import example_device'
+
+[testenv:lower-constraints]
+deps =
+  -c{toxinidir}/lower-constraints.txt
+  -r{toxinidir}/test-requirements.txt
+  -r{toxinidir}/requirements.txt

zuul.d/project.yaml

@@ -1,9 +1,10 @@
 - project:
     templates:
-      - openstack-python3-xena-jobs
-      - openstack-cover-jobs
-      - publish-openstack-docs-pti
       - check-requirements
+      - openstack-cover-jobs
+      - openstack-lower-constraints-master-branch-jobs
+      - openstack-python3-xena-jobs
+      - publish-openstack-docs-pti
       - release-notes-jobs-python3
     check:
       jobs: